The Efficient Home Forum

Running a fixed speed heat pump from Kensa. They have high starting currents and poor efficiency below 6 minutes.

There is a very good report here on how inefficient it is to run the heat pump for < 10 minutes.
https://assets.publishing.service.gov.u ... _pumps.pdf

So with the Evohome, i have set the maximum # of starts per hour to 3. Which is fine doing a good job of limiting how many starts.

Its the minimum run time to the heatpump(boiler) that is limiting my efficiency. The maximum allowed is 5 minutes. I would like to set it for 10 minutes to eliminate this shortcycling when all rooms are close to target (Most of the time at start/end of winter season).

With underfloor heating in all rooms and a GSHP, 5 minute cycles is just too short. These systems need less but longer cycles to be efficient.
These systems have expensive buffer tanks added to make sure the heatpump can run for its designed minimum period, but evohome is cutting it short, making most of that redundant.

Any ideas how i can work around this limiting 5 minute on-time ?

Example of 2 hours at low load (all rooms close to target). Evohome uses all of it maximum 3 x start per hour, and its maximum 5 mins per start. So 15 mins / hour, or 25% run time.
It needs more flexibility: 1 x 10 minute run or even 1 x 15 minute run. My hands are tied by Evohome and its frustrating.

Isn't there a setting for minimum on time?
This thread suggests there is
http://theevohomeshopforum.co.uk/viewto ... f=4&t=3868

I have a similar question. I currently use Evohome with a boiler, and I plan to get a heatpump

There is almost no information I can find about how Evohome works with a heatpump, but I did find this https://phpionline.co.uk/feature-articl ... p-systems/
It says that the author set one cycle per hour, minimum run time 20 minutes and minimum off time 10 minutes. How did he do that??

My controller is set up for a boiler, and the lowest cycle rate I can set is 3 per hour, and the highest minimum time is 5 minutes. If I change the 'Appliance Control' to 'heat pump relay' I wonder if it opens up a different set of parameters and/or different limits? Have you tried that @geoheated?

Has anyone else used the "heat pump relay" setting for Appliance Control, and does anyone know how this affects the various system parameters?

Peter 269 I am just having a heat pump installed and I confirm that removing the BDR91T controller as a boiler on and off and then rejoining ii as a Heatpump relay allows you to set system parameters of cycle rate 1hr min on time 20mins min off time 10 mins
I'll see how we get on with those settings and report back.